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What is Physics?

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What is Physics?

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**Feb 28, 2009 Merlion hit by lightning**

A lightning bolt struck the Merlion statue at about 4.30pm yesterday. The national icon at One Fullerton facing the Singapore River lost part of its top left mane and is believed to have its right ear chipped. About 20 to 30 people nearby, including tourists, ran helter-skelter in the pouring rain when debris from the Merlion's head went flying. Some ran to safety in the nearby shops and cafes. The fragments fell onto the patio at One Fullerton and the Singapore River Cruise counter near the Merlion. Nobody was hurt. Eyewitness Ms Rina Toh, 17, a barista at The Coffee Bean and Tea Leaf at One Fullerton, said: 'I saw a bright Z-shaped lightning bolt, and it was a lot bigger than usual.' She was standing at the counter and could see the Merlion.

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What is Physics? Physics is the study of the natural world around us – from the very large, such as the solar system, to the very small, such as the atom.

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**Physical Quantities, SI Units and Measurement**

In the quest to understand nature, scientists use physical quantities to describe the world around us. Physical Quantities, SI Units and Measurement Chapter 1

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**At the end of this chapter…**

You should be able to: show understanding that all physical quantities consist of a numerical magnitude and a unit recall the following base quantities and their units: mass (kg), length (m), time (s), current (A), temperature (K) use the following prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units: nano (n), micro (μ), milli (m), centi (c), deci (d), kilo (k), mega (M)

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**At the end of this chapter…**

You should be able to: show an understanding of the orders of magnitude of the sizes of common objects ranging from a typical atom to the Earth describe how to measure a variety of lengths with appropriate accuracy by means of tapes, rules, micrometers and calipers, using a vernier scale as necessary describe how to measure a short interval of time including the period of a simple pendulum with appropriate accuracy using stopwatches or appropriate instruments

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Cubit

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**Why do We Need to Measure Things?**

Let’s do this as a class… Work in groups of two Compare the length between the elbow to the first finger tip.

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**Why do We Need to Measure Things?**

Are they the same?

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**Physical Quantities and SI Units**

Base Quantity Name of SI unit Symbol for SI Unit Length metre m Mass kilogram kg Time second s Electric Current ampere A Temperature kelvin K Intensity candela cd Amount of Substance mole mol

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Physical Quantities A physical quantity when measured may be described in terms of A number Its unit of measurement actual length = m

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Physical Quantities What is your height? 2 m quantity unit

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Physical Quantities Mass – unit of measurement, kilogram (kg)

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Physical Quantities Time – unit of measurement, second (s)

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Physical Quantities What are some problems we might face in our daily lives if there are no standard measurements?

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**Do You Know??? 1 400 000 000 m 1.4 Gm (gigametre) 0.0002 m**

Diameter of the Sun Thickness of a strand of hair m m 1.4 Gm (gigametre) 0.2 mm (millimetre)

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**Prefixes for SI units 10 giga- G 10 mega- M 10 kilo- k 10 deci- d 10**

Factor Prefix Symbol 10 9 giga- G 10 6 mega- M 10 3 kilo- k 10 - 1 deci- d 10 - 2 centi- c 10 - 3 milli- m 10 - 6 micro- 10 - 9 nano- n

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**Prefixes Exercise 1 Express the following quantities**

in their respective SI unit. One kilometer = 1000m or 103m One microsecond = s or 10-6s One centimeter = 0.01m or 10-2m One gram = 0.001kg or 10-3kg Factor Prefix Symbol 109 giga- G 106 mega- M 103 kilo- k 10-1 deci- d 10-2 centi- c 10-3 milli- m 10-6 micro- 10-9 nano- n

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**Prefixes Exercise 1 One miligram = 0.001g or 10-3g =10-6 kg**

Factor Prefix Symbol 109 giga- G 106 mega- M 103 kilo- k 10-1 deci- d 10-2 centi- c 10-3 milli- m 10-6 micro- 10-9 nano- n One miligram = 0.001g or 10-3g =10-6 kg One millisecond = 0.001s or 10-3s One minute = 60s One hour = 3600s

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**What does SI units mean? Système International**

International System of Units

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**Measurement of Length m metre**

The SI unit for length is ( ) Other units for length: m metre millimetre (mm), centimetre (cm), kilometre (km)

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**Accuracy of Instruments**

Measurement of Length Range Suitable Instruments Accuracy of Instruments Several metres (m) Several centimetres (cm) Between 1cm to 10cm Less than 2 cm Measuring Tape 0.1 cm (or 1 mm) Metre/Half- metre Rule 0.1 cm (or 1 mm) Vernier Calipers 0.01 cm (or 0.1 mm) Micrometer Screw Gauge 0.001 cm (or 0.01 mm)

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**Measurement of Length Metre rule: Measuring Tape**

- Length of classroom, car, corridor Metre rule: Length of desk, book

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**Measurement of Length Parallax Error What is Parallax Error?**

It is the error which arises due to incorrect positioning of the eye. 2.7 cm correct 3.0 cm wrong cm 1 2 3

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**Measurement of Length Parallax Error How do we avoid Parallax Error?**

Always place the eye vertically above the mark being read. OR Place the eye in level with the mark being read. 3.0 cm wrong 2.7 cm correct cm 1 2 3

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**Vernier Calipers French scientist Pierre Vernier(1580-1637)**

Accuracy: 0.01 cm (or 0.1 mm)

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**How to read off the Vernier Caliper?**

11mm 0.7mm mm Measured Value Reading = 11 mm mm = 11.7 mm

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**Vernier Calipers Its structure and its application**

The inside jaws is used to measure internal diameter of test-tube, ring etc. In main scale, reading = 1.90 cm in vernier scale, reading = 0.01 cm the actual reading = 1.91 cm

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**Vernier Calipers Its structure and its application**

The outside jaws is used to measure small length, diameter of test-tube etc. main scale reading = 4.20 cm vernier scale reading = 0.06 cm Actual reading = 4.26 cm

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Exercise 1 mm Reading = 19 mm mm = 19.4 mm

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Exercise 2 mm Reading = 4 mm mm = 4.7 mm

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Exercise 3

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Exercise 4

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Exercise 5 mm Reading = 12 mm mm = 12.6 mm

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Exercise 6 mm Reading = 7 mm mm = 7.5 mm

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**vernier scale (movable)**

Vernier Calipers Zero Error (Vernier Calipers) Positive Zero Error 10 5 main scale (fixed) vernier scale (movable) 0.1mm +0.1 mm Zero Error = mm If the observed reading = 32.4mm, then Actual measurement = Observed reading – Zero error = mm = cm +0.1 (+0.1) 32.3

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**vernier scale (movable)**

Vernier Calipers Zero Error (Vernier Calipers) Negative Zero Error 10 main scale (fixed) 0.1mm vernier scale (movable) 5 10 - 0.2 mm Zero Error = mm If the observed reading = 32.4 mm, then Actual measurement = Observed reading – Zero error = mm = mm - 0.2 (-0.2) 32.6

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**Micrometer Screw Gauge**

Accuracy: cm (or 0.01 mm) Smaller length, such as diameter of thin wire, thickness of a piece of paper etc can be measured by micrometer screw gauge.

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**Micrometer Screw Gauge**

3 mm 0.09 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 3.0 0.09 3.09 0.309

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**Micrometer Screw Gauge**

0.30 mm 5.5 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 5.5 0.30 5.80 0.580

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**Micrometer Screw Gauge**

0.06 mm 3.5 mm Sleeve reading = mm Thimble reading= mm Reading = mm Reading = cm 3.5 0.06 3.56 0.356

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Exercise 1 11.5mm 0.25mm Reading = 11.5 mm mm = mm

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Exercise 2 15 20 30 25 Reading = 20.5 mm mm = mm

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**Micrometer Screw Gauge**

Zero Error (Micrometer Screw Gauge) Positive Zero Error +0.02 mm Zero Error = mm If the observed reading = 2.37mm, then Actual measurement = Observed reading – Zero error = mm = mm +0.02 (+0.02) 2.35

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**Micrometer Screw Gauge**

Zero Error (Micrometer Screw Gauge) Negative Zero Error mm Zero Error = mm If the observed reading = 2.37mm, then Actual measurement = Observed reading – Zero error = mm = mm - 0.03 (- 0.03) 2.40

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**Measurement of Time Two types: SI unit of time: second, s**

Stopwatches are used to measure short intervals of time. Two types: Digital stopwatch Analogue stopwatch SI unit of time: second, s

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**Accuracy of Instruments**

Measurement of Time Instruments Usage Accuracy of Instruments Watch/Clock hrs, mins, sec Analogue Stopwatch mins, sec Digital Stopwatch Atomic Clock about s - Pendulum Clock Radioactive decay clock thousand of years 1 s 0.1 s 0.01 s

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**Measurement of Time Watch/Clock**

used for measuring long intervals of time most modern watches depend on the vibration of quartz crystals to keep time accurately the energy that keeps these crystals vibrating comes from a small battery many watches still make use of coiled springs to supply the needed energy

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**Measurement of Time Stopwatch (Analogue/Digital) Digital Stopwatch**

A stopwatch is used to measure short intervals of time. stopwatches (analogue and digital) Digital Stopwatch accuracy = 0.01 s Analogue Stopwatch accuracy = 0.1 s

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**Measurement of Time Atomic Clock**

Atomic clock also work on oscillation. The big difference between a standard clock in your home and an atomic clock is that the oscillation in an atomic clock is between the nucleus of an atom and the surrounding electrons. They even keep time better than the rotation of the Earth and the movement of the stars. Without atomic clocks, GPS navigation would be impossible, the Internet would not synchronize, and the position of the planets would not be known with enough accuracy for space probes and landers to be launched and monitored.

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**Measurement of Time Pendulum Clock**

clocks make use of a process which is a regularly repeating motion (oscillations), such as the swing of a pendulum such oscillations are very regular so period is regular most modern clocks depend on the vibration of quartz crystals to keep time accurately in clocks that are wound up, elastic potential energy is stored in coiled springs

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What is a pendulum? A small object suspended by a piece of string or tread is called a simple pendulum. The distance from the centre of the pendulum bob to the point of suspension is called the length of the pendulum. One complete to and fro movement of the pendulum is called an oscillation. The time taken for one complete oscillation is called the period. The distance between the rest position of the pendulum and the extreme point of its oscillation is called the amplitude.

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**Diagram of a Pendulum Amplitude Length of Pendulum From B to C A C B**

Oscillation From A to B to C and back to B to A

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**Finding the Period of a Pendulum**

To find the period: 1. Take the total time for 20 oscillations. Why 20? 2. Repeat 2 more times. 3. Calculate the average time for 20 oscillations. 4. Divide by 20 to obtain the period.

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**What Affects the Period of a Pendulum?**

Mass? Amplitude? Length?

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**Simple Pendulum When the length increases, the period increases.**

When the length decreases, the period decreases. When the mass of the bob increases/decreases, there is no effect on the period.

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Simple Pendulum When the amplitude of the bob increases/decreases, there is no effect on the period. When the same experiment is done on the moon, the period increases.

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Pendulum Exercise The time taken for a pendulum to swing from rest position A to B is 0.8s. What is the time taken for the pendulum to make 20 oscillations?

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